1,361 research outputs found
Turing Instability in a Boundary-fed System
The formation of localized structures in the chlorine dioxide-idodine-malonic
acid (CDIMA) reaction-diffusion system is investigated numerically using a
realistic model of this system. We analyze the one-dimensional patterns formed
along the gradients imposed by boundary feeds, and study their linear stability
to symmetry-breaking perturbations (Turing instability) in the plane transverse
to these gradients. We establish that an often-invoked simple local linear
analysis which neglects longitudinal diffusion is inappropriate for predicting
the linear stability of these patterns. Using a fully nonuniform analysis, we
investigate the structure of the patterns formed along the gradients and their
stability to transverse Turing pattern formation as a function of the values of
two control parameters: the malonic acid feed concentration and the size of the
reactor in the dimension along the gradients. The results from this
investigation are compared with existing experiments.Comment: 41 pages, 18 figures, to be published in Physical Review
Association of drusen deposition with choroidal intercapillary pillars in the aging human eye
PURPOSE. To determine the pattern of drusen accumulation with age and to investigate the initial sites of deposition and their relationship to choroidal capillaries in human donor eyes from the eye bank of Moorfields Eye Hospital.METHODS. Wholemounted, hydrated preparations of the choriocapillaris and Bruch's membrane from donor eyes ranging from 42 to 95 years, with or without retinal pigment epithelium (RPE), were examined by conventional and confocal microscopy. Drusen were visualized by their autofluorescence.RESULTS. In all age groups studied autofluorescent drusen were present at the equator but were not found centrally where the vascular architecture is different, being tubular rather than a honeycomb pattern. Autofluorescing drusen were strongly associated with the lateral walls of the choriocapillaris (an area commonly known as the intercapillary pillars of the choriocapillaris (P = 0.028; Wilcoxon signed ranks test). Nonfluorescing drusen were occasionally seen centrally, but were not easily identified, and because of their large size, their localization with respect to capillary walls was not possible.CONCLUSIONS. These results strongly support the notion that autofluorescent drusen are not randomly distributed and have a specific spatial relationship to choroidal vessel walls. That equatorial drusen fluoresce, whereas central drusen do not, suggests that they may have different chemical compositions at the two sites and possibly different significance in age-related macular disease
TRESK background potassium channel is not gated at the helix bundle crossing near the cytoplasmic end of the pore.
Two-pore domain K+ channels (K2P) are responsible for background K+ currents and regulate the resting membrane potential and cellular excitability. Their activity is controlled by a large variety of physicochemical factors and intracellular signaling pathways. The majority of these effects converge on the intracellular C-terminus of the channels, resulting in the modification of the gating at the selectivity filter. Another gating mechanism, the activation gate at the helix bundle crossing is also well documented in other K+ channel families, however, it remains uncertain whether this type of gating is functional in K2P channels. The regulation of TWIK-related spinal cord K+ channel (TRESK) is different from the other K2P channels. Regulatory factors acting via the C-terminus are not known, instead channel activity is modified by the phosphorylation/dephosphorylation of the unusually long intracellular loop between the 2nd and 3rd transmembrane segments. These unique structural elements of the regulation lead us to examine channel gating at the bundle crossing region. Ba2+ was applied to the intracellular side of excised membrane patches and the characteristics of the channel block were determined. We compared the kinetics of the development of Ba2+ block when the channels were phosphorylated (inhibited) or dephosphorylated (activated) and also in different mutants mimicking the two functional states. Neither the phosphorylation/dephosphorylation nor the point mutations influenced the development of Ba2+ block, suggesting that the conformational changes of the bundle crossing region do not contribute to the phosphorylation-dependent gating of TRESK
The proton structure function and a soft Regge Dipole Pomeron: a test with recent data
A recently published soft Regge Dipole Pomeron model intended for all and
is proved to give a good agreement with (non fitted) recent HERA data
from ZEUS (SVX95) on the protonstructure function at low
and low . The model also reproduces (without fit) the recently estimated
experimental derivatives and
in a wide and
-region.Comment: 5 pages (LaTeX), 4 figures (Encapsulated PS
Growth of the golden spined loach [Sabanejewia aurata (Filippi, 1865)] in River Tisza (Eastern Hungary)
Two ('plus one')-dimensional simulation of pellet cloud evolution in the poloidal plane with a prescribed neutral particle source strength
New possibilities of old soft pomeron in DIS
A traditional Regge model with a -independent Pomeron intercept closed
(or equal) to one is constructed in order to describe the available data on the
proton structure function. A Dipole Pomeron model which does not explicitly
violate unitarity is developed and investigated. An excellent agreement with
the 1209 data is found () in the whole kinematical domain
investigated by experiments. A comparison of the model with already existing
ones is made. The , slopes and the effective intercept are discussed
as and functions.Comment: 19 pages LaTeX, 10 eps figures included, one of figure captions is
correcte
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